For fixation of bones (i.e., fusion and unification of bones) in bone surgeries, such as repositioning of bones after spinal fractures, bone grafting, and the like, the bones must, in order for their fixation, be kept tightly held together, so that they may not be displaced before their fusion is completed. Recently, for the purpose of achieving such holding, cables made of high-strength synthetic fibers, like high molecular weight polyethylene (referred to as “bone-tying cables” in the present invention), have been used.
In a surgery employing bone-tying cables, as FIG. 1 schematically illustrates a typical manner of tying with an above-mentioned cable which is made of synthetic fibers, such a procedure is followed that bones to be held together (shown in the form of round bars) are first tied with a loop of the bone-tying cable (together with a rod, a hook or the like to serve as a splint, if necessary) (FIGS. 1(a)-(f)), and then,
(1) while the knot (provisional knot) shown in FIG. 1(f) is supported, the two arms of the cable extending from it are held together and pulled tightly so that the size of the loop is reduced and the bones thereby are fastened to each other, and, after the tension of the loop has been increased up to a required level, then keeping that condition, the knot is immobilized with, e.g., an adhesive or an attachment, or
(2) a provisional knot is formed starting from the condition as depicted in FIG. 1(g) by pulling the two arms in the directions indicated with the arrowheads, and, the two arms of the cable extending therefrom are then pulled firmly in both lateral directions so that the size of the loop is reduced and the bones thereby are fastened to each other, and, after the tension of the loop has been increased up to a required level, then keeping the tension, the knot is immobilized by means of additional knots or an adhesive or the like, as required to prevent it from slipping.
It is required that the above fastening with the bone-tying cable must create a strong tension (e.g., 5-10 kgf) in the cable which forms the loop. In order to overcome the frictional force between the fibers of the cable within the provisional knot, thereby causing cable portions to slip with one another and thus reducing the size of the loop to achieve such a strong tension in it, the two arms extending from the provisional knot must be pulled with a greater tension. A device is sold as a product to enables this, which is a “bone-tying cable tightening device” described in Patent No. 3721189 (Patent Literature 1), [Tighting Gun [MAH], mftd. by Alfresa Pharma Corporation].
While the above device can be used repeatedly for an extended period of time, through repeated washing and sterilization performed after each use, it requires regular maintenance by its producer, since it is a device used in a surgery. Thus, the products delivered to each medical facility must be kept under control, each by separately setting the timing for maintenance. For maintenance, each device must be recovered from the medical facility, and after its disassembling, examination, fine adjustment, washing and the like, be returned to the medical facility which owns it. The process of maintenance, including a series of actions like schedule management, recovery, examination, and adjustment, as well as returning of the device, requires a lot of manpower and its cost-efficiency is very low. Furthermore, because of its presumed repetitive and extended use, this type of device is made, almost entirely, of metal in order that it should stand through such use, and, in consequence, is costly to produce. Thus it is difficult to curtail the total cost per device, including the cost for its maintenance. Further, it also is a trouble that, since it is impossible for its producer to directly know in what manner, e.g., how often, a device has been used at each facility, it is not an easy matter to determine whether the frequency of maintenance set for each device is appropriate or not. Furthermore, the device has another drawback that, as it is made, almost entirely, of metal and therefore is heavy, some operators feel its weight as a burden.